Facilitation of acoustic responses of cartwheel neurons of the cat dorsal cochlear nucleus

Responses to clicks were increased in cartwheel cells of the dorsal cochlear nucleus of cats after pairing presentations of the clicks with local iontophoretic delivery of glutamate. The cells were identified by bursting discharges, and were recorded intracellularly in vivo. The findings indicate that inhibitory interneurons such as cartwheel cells can participate in complex adaptive acoustic signal processing. Each cell displayed doublet discharges of > 800 Hz. In 70% of the cells, some of the doublet discharges reached rates > 1000 Hz.     

The brain renin-angiotensin system contributes to the hypertension in mice containing both the human renin and human angiotensinogen transgenes

We have previously shown that mice transgenic for both the human renin and human angiotensinogen genes (RA+) exhibit appropriate tissue- and cell-specific expression of both transgenes, have 4-fold higher plasma angiotensin II (AII) levels, and are chronically hypertensive. However, the relative contribution of circulating and tissue-derived AII in causing hypertension in these animals is not known. We hypothesized that the brain renin-angiotensin system contributes to the elevated blood pressure in this model. To address this hypothesis, mean arterial pressure (MAP) and heart rate were measured in conscious, unrestrained mice after they were instrumented with intracerebroventricular cannulae and carotid arterial and jugular vein catheters. Intracerebroventricular administration of the selective AII type 1 (AT-1) receptor antagonist losartan (10 microgram, 1 microL) caused a significantly greater peak fall in MAP in RA+ mice than in nontransgenic RA- controls (-29+/-4 versus -4+/-2 mm Hg, P<0.01). To explore the mechanism of a central renin-angiotensin system-dependent hypertension in RA+ mice, we determined the relative depressor responses to intravenous administration of the ganglionic blocking agent hexamethonium (5 mg/kg) or an arginine vasopressin (AVP) V1 receptor antagonist (AVPX, 10 microgram/kg). Hexamethonium caused equal lowering of MAP in RA+ mice and controls (-46+/-3 versus -52+/-3, P>0.05), whereas AVPX caused a significantly greater fall in MAP in RA+ compared with RA- mice (-24+/-2 versus -6+/-1, P<0.01). Consistent with this was the observation that circulating AVP was 3-fold higher in RA+ mice than in control mice. These results suggest that increased activation of central AT-1 receptors, perhaps those located at sites involved in AVP release from the posterior pituitary gland, plays a role in the hypertension in RA+ mice. Furthermore, our finding that both human transgenes are expressed in brain regions of RA+ mice known to be involved in cardiovascular regulation raises the possibility that augmented local production of AII and increased activation of AT-1 receptors at these sites is involved.     

The murine anti-human common gamma chain monoclonal antibody CP.B8 blocks the second step in the formation of the intermediate affinity IL-2 receptor

A murine monoclonal antibody, CP.B8, specific for the extracellular portion of the human common gamma (gammac) chain, and its Fab fragment are shown to block the binding of IL-2 to COS-7 cells transfected with the cDNA for the full-length IL-2 receptor beta (IL-2Rbeta) and gammac chains, components which together comprise the intermediate affinity IL-2 receptor (IL-2R) expressed on the surface of resting T cells, NK cells, and on certain intestinal epithelial cells. To investigate the mechanism of this inhibition, the extracellular portions of the IL-2Rbeta and gammac chains were expressed and purified, and their interactions with each other and with IL-2 were studied by gel filtration and by surface plasmon resonance (SPR). By gel filtration, a stable ternary complex was formed by association of the three proteins, while no stable binary complexes were detected between any two of the three proteins. By SPR analysis, IL-2 was shown to associate rapidly with IL-2Rbeta, forming a binary complex with an equilibrium dissociation constant (Kd) of 800 nM, which permitted subsequent association of the gammac chain. Dissociation of the IL-2/IL-2Rbeta/gammac chain complex was significantly slower than dissociation of the IL-2/IL-2Rbeta complex. Using these model systems, we tested the ability of mAb CP.B8 to inhibit the association of the gammac chain with IL-2 and IL-2Rbeta. By gel filtration, mAb CP.B8 formed a stable complex with the gammac chain, preventing its association with IL-2 and IL-2Rbeta. MAb CP.B8 was also capable of dissociating the gammac chain already complexed with IL-2 and IL-2Rbeta. SPR analysis confirmed these findings and showed, in addition, that the Fab fragment of CP.B8 was also capable of inhibiting the association of the gammac chain with the IL-2/IL-2Rbeta complex. We conclude that mAb CP.B8 blocks the second step in the formation of the intermediate affinity IL-2R on the surface of transfected COS-7 cells by binding at or close to a region on the gammac chain that is involved in contact with IL-2 and/or IL-2Rbeta.